Selective Removal of Impurities from Molten Aluminum

Abstract

The present disclosure concerns using microstructural engineering techniques to remove or reduce impurity elements from molten aluminum alloys, such as scrap. The impurities are removed by cooling molten aluminum, resulting in the formation of impurity-rich intermetallic compounds containing only one or more impurity elements as solid inclusions. Subsequent removal of impurity-rich intermetallic sediments by decantation, centrifuge, and filtration techniques can provide an economical method for removing the desired amount of impurities to meet the product specifications.

We claim: 
     
         1 . A process for producing an aluminum alloy comprising:
 a.) melting an aluminum source at >725-° C. to obtain a melt;   b.) adding to the melt with an alloying element at at least >725° C., wherein the alloying element is selected from the group consisting of chromium, vanadium, yttrium, cerium, manganese, or at least two thereof;   c.) lowering the temperature of the melt to a lowered holding temperature of about 615° C. to about 725° C.;   d.) maintaining melt at the lowered holding temperature for at least about 15 minutes; and   e.) removing precipitated impurity-rich intermetallics from the melt to provide the aluminum alloy.   
     
     
         2 . The process of  claim 1 , wherein alloying element comprises 0.3 to 5% by weight of the melt. 
     
     
         3 . The process of  claim 1 , wherein the aluminum source comprises a wrought aluminum and/or a cast aluminum. 
     
     
         4 . The process of  claim 1 , wherein holding the melt in step (b) is for a period of time of at least 15 minutes. 
     
     
         5 . The process of  claim 1 , wherein the temperature of the melt is lowered to the lowered temperature at a cooling rate of about 5° C. to about 15° C. per minute. 
     
     
         6 . The process of  claim 1 , wherein the scrap aluminum comprises an iron content of at least 0.2% by weight. 
     
     
         7 . The process of  claim 1 , wherein the scrap aluminum comprises a silicon content of less than 3% by weight. 
     
     
         8 . The process of  claim 1 , wherein the scrap aluminum comprises a silicon content of at least than 3% by weight. 
     
     
         9 . The process of  claim 1 , wherein the alloying element comprises manganese. 
     
     
         10 . The process of  claim 1 , wherein the alloying element comprises chromium. 
     
     
         11 . The process of  claim 1 , wherein in the alloying element comprises cerium. 
     
     
         12 . The process of  claim 1 , wherein the alloying element comprises yttrium. 
     
     
         13 . The process of  claim 1 , wherein the alloying element comprises vanadium. 
     
     
         14 . The process of  claim 1 , wherein the alloying element comprises magnesium and chromium. 
     
     
         15 . The process of  claim 1 , further comprising raising the silicon content of the melt. 
     
     
         16 . The process of  claim 1 , wherein the melt is mixed by mechanical stirring. 
     
     
         17 . The process of  claim 1 , wherein the lowered holding temperature is of about 615 to about 650° C. 
     
     
         18 . The process of  claim 1 , wherein the cooling rate allows for formation of iron-manganese impurity-rich intermetallics to initiate. 
     
     
         19 . An impurity-rich intermetallic aluminum alloy comprised of aluminum, 0.01 to 10 wt. % iron, 0.01-10 wt. % manganese, and 0.2-2.0 wt. % of an alloying element selected from the group consisting of chromium, cerium, magnesium, vanadium, yttrium, manganese or a combination thereof. 
     
     
         20 . The impurity-rich intermetallic aluminum alloy of  claim 19 , further comprising 0 to 12 wt. % silicon.